Thermal plug cut-out



.lIlI

Patented Sept. 11, 1928.

UNITED STATES PATENT' i OFFICE.

EARL K. CLARK, OFMANSFIELD, OHIO, ASSIGNOR TO WESTINGHOUSE ELECTRIC .6s MANUFACTURING COMPANY, A CORPORATION OE PENNSYLVANIA.

THERJMIAL PLUG- CUT-OUT.

Application led April 2, 1927. Serial No. 180,465.

My invention relates to thermal ciitouts and particularly to thermal cutouts for use in motor circuits for the purpose of opening such circuits under overload conditions.

An object of my invention is to provide a thermal cutout of the screw-plug type having relatively low current capacity, for instance, one ampere or a fraction thereof, and which may be adjusted to interrupt the circuit after the overload has mined time period.

Another object .of my invention is to pro-A vide a thermal cutout having the abovenoted characteristics wherein the cutout device may be renewed after rupture thereof has occurred, the cutout device comprising a removable composite refill that is adapt-ed to interiupt the circuit under predetermined eurrent conditions by causing separation of parts of the refill. i

A further object of my invention is to provide a refill for thermal cutouts that -shall be inexpensive to manufacture and which may be readily assembled and in which the capac` ity thereof. may be varied by variations in the length of theA heating conductor constituting a part of the refill. These and other objects that will be mad apparent throughout the further description ofmy invention are attained by means o f the apparatus hereinafter described, and illustrated in the accompanying drawings, Where- Figure 1 is a longitudinal sectional view through a cutout device embodying features of my invention; Fig. 2 is a plan view of the device shown in Fig. 1. the cover being removed; l

Fig. 3 is a top pla-n view of the refill; and Fig. Il is a longitudinal sectional view through the refill, taken on'the line IV--IV of Fig. 3.

In copending applications, Serial Nos.

614,379 and 614,381 filed January 23, 1923,l

and vapplication Serial No. 614,378, file d September 18, 1926, by Maurits J. Sandin and assigned to the Westinghouse Electric and Manufacturing Company ot` East Pittsburgh. Pennsylvania, thermal cutoutsare disclosed having screw-plug housings similar to the housing illustrated in Fig. 1.

My invention relates to an improved form of cutout refill and no claim is made to the specific form of housing illustrated.

prevailed for a predeterf/ The housing for the cutout comprises anl insulating casing 5 made of porcelain or other insulating material and having a reduced cylindrical portion 6, .surrounded by a metal threaded screw shell or terminal member 7 that engages within a threaded socket or receptacle 'of the usual type (not shown). The casing 5 is provided with an interior bore 8 terminating in an enlarged chamber' 9 for receiving a Contact washer 11 that is mounted for longitudinal movement therein.

The reduced portion 6 of the'casing is provided with a metal tubular contact member 12 that is retained in position by having its inner end peened outwardly to engage the inner inclined'wall of the bore 8, asindicated in Fig. 1. f i

The Washer 11 is conductively connected to the terminal shell 7 by means of an annular flexible metal strip 13 that is riveted,.at one end,.to the underside of the Washer 11 and, at the other end, to a conductor strip 111 that extends through a channel 15 in the casing and is welded to the threaded terminal 7. The outward movement of the washer 11 is limited by a strap 16 that is Welded to the terminal shell 7 and is provided with an extension 17 that is bent inwardly.

The washer 11 is normallyI biased to its outermost position by means of a spring 18 disposed wit-hin the bore 8 between the annularv inner end 19 of the member 12 and the inner endof the insulating sleeve21 which engages the inner side of the washer 11.

The contact terminal 12 is designed to engage a. conta-ct member within the receptacle (not shown) and current is conducted. between the terminal 12 and the terminal shell 7 through the medium of a refill 22 that is detac-hably secured within the casing by means vof. a screw 23 carried by the terminal 12.

Normally, current flows from the terminal 12 through the thermal-responsive cutout or refill 22 to the washer 11 and thence to the terminal shell 7 through the conductor stiap 14. When the refill becomesv ruptured by reason of overload conditions, the spring 18 forces the wash-er 11 to its outermost posi'- tion and thus separates the parts of the refill and interrupts the circuit.

The chamber 9 is closed by means of an annular threaded cap 24 that is screwed upon the enlarged portion of the casing 5 and serves t0 retain a transparent m ica win dow 25 a heating conductor `of,

with a central opening `disc 27, respectively.

"in the cover.

Considerable diliculty has been experienced heretofore in providing a cutout refill of fractional-ampere capacity having suiiicient rigidity to withstand service conditions.

By reason of my improved form of reill, ample physical strength may be employed in a fractionalampere circuit which Will cause interruption thereof Within a predetermined time period after t-he occurrence of relatively small overload conditions.

The cutout refill comprises a metal disc 27 which may be of any desired thickness and heat-storing capacity. The disc is provided for receiving theend of a steel t-ube 29 that is soldered to the washer, as indicated in Fig. 4, by means of solder 31. y

The attached end of the tubular member 29 is provided with a longitudinal slot '32 that registers with a radial slot 33 in the disc 27. The purpose of the slots 32-and 33 is-toy permit of the assembly of aheating conductor 34 that extends through the tubular member 29 and is coiled, as a helix, about its exterior, as indicated in Fig. 4. Y

The heating conductor comprises a piece of relatively high-resistant Wire, such as nichrome, rent-insulating material, preferably asbestos.

The heating conductor 34 is assembled upon the tubular member 29 by inserting it at the unslot-ted end and through the bore and the slots 32 and 33 in the tube. 29 and The external portion is then helically Wound upon the exterior of the tube, as indicated in Fig. 4. The end 36 is then welded to the exterior of the tube to form a conductive connection between them.

Since a relatively long heating conductor may thus be employed, a relatively heavy conductor may be used which is of sufficient strength to withstand the stresses imposed by K the spring 18 which tends to separate the tube i conductor, constitutes a heat-storage yof considerable thermal capaclty. Conse- 60.

29 from the disc 27. A relatively heavy heating Wire also possesses a greater overload capacity, enabling the reiill to function properly on loads above the ampere capacity of low-rated current devices.

lVhen an abnormal current prevails in the circuit, the heating conductor radiates heat which is transmitted to the metal tubular member 29 vvhich, combined with the heating member quently, a slight increase in temperature in the heating conductor and the tubular member will overcome the cooling action of the vdise 27 and the Washer 11 and raise the temperature of the solder 31 to the fusing point,

that has a coating of heat-and-curat which time the spring 18 causes the disc 27 to be separated from the tubular member 29 with a 'snap action. i

The circuit may be restored by removing the casing. or cutout plug from its receptacle, (not shown) releasing the screw-23 from engagement with the end of the conductor 34 to permit of removal of the tube 29 and the heating conductor. A new refill may then be inserted-and the screw 23 tightened when the refill has been pressed inwardly sufficient to move the terminal `Washer 11 to its innermost position, shown in Fig. 1.

lVhile I have shown anddescribed a particular form of my invention, changes may be Aeffected therein Without departing from the spirit and scope thereof, as set forth in the appendedclaims.

I' claim as my invention: y

1. A composite thermal-responsive refill for a circuit cutout comprising a pair of separable members joined by fusible metal, one of which larV member -and wound about the exterior thereof and having its free end extending through the tubular member. and constituting a terminal member.

l2. -A composite thermal-responsive refill for a circuit cutout comprisinvr a pair of separable members joined by fusible metal, one ofwhich constitutes a terminal member and the other a tubular heat-storing member, and aheating conductor connected, at one end, to the tubular member and Wound about the exterior thereof and having its free end extending through the tubular member and constituting a terminal member, the said conductorlbeing coated with a heat-insulating materia 3. A composite,thermal-responsive refill for a circuit cutout comprising a pair of separable members joined by fusible metal,.one of which constitutes a terminal member and the other a tubular heat-storing member, and4 a heating conductor connected at one end to the tubular member and wound about the exterior thereof and having its free end extending through the tubular member and constituting a terminal member, the 'said conductor being coated with current-insulating material.

4. A thermal-responsive refill for a circuit cutout comprising a metal disc having a slot extending inwardly from the periphery there- E, K. CLARK.r 

